Drop mass compaction of soil

ABSTRACT

A soil compaction apparatus includes a drop mass soil compactor having a mass and a lift assembly that repeatedly raises the mass above a soil surface and then drops it to apply impacts to the soil surface. The apparatus also has a sensor arranged to provide periodic indications of one or more instantaneous properties of the soil. The apparatus also includes a controller that received a signal from the sensor and controls the lift assembly to attain desired, pre-programmed soil properties based on a number of impacts, energy imparted to the soil at each impact or frequency if impacts of the mass.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/IB2003/002578, filed Jul. 1, 2003, which was published in theEnglish language on Jan. 8, 2004, under International Publication No. WO2004/003301 A1, and the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

This invention relates to methods and apparatus for achieving drop masssoil compaction and for monitoring soil properties.

There are numerous applications where it is necessary to compact arelatively small area of soil but where the use of conventional soilcompaction machinery, typically employing rollers of one type oranother, is inappropriate. One important example is in the compaction ofsoil adjacent bridge abutments, where limited space makes it impossibleto compact with conventional large rollers or other machines. Anotherexample is in the compaction of soil in relatively narrow trenches forpipes, strip foundations or the like. Yet another example is in roadmaintenance where local failure of a section of a road may have takenplace in a relatively small area.

Although small vibratory rollers and impactors are available and arewidely used in such applications, the level of soil compaction and thedepth of compaction influence which can be achieved with such devices islimited. The result is often that undue settlement and or structuralfailure can take place after a relatively short period of time.

It has been proposed to use drop mass soil compaction to achievecompaction of soil in the kind of situations envisaged above. In dropmass compaction, a substantial mass is repeatedly raised and dropped toapply impacts to the soil surface for the purposes of compacting it. Formore detail about one known drop mass soil compactor, reference may forinstance be made to International Patent Application Publication No. WO00/28154 A1 (Cook, et al.).

Although the principles of drop mass soil compaction are sound, it isfelt that greater control over the compaction process is required toenable this type of compaction technology to achieve its full potential.

BRIEF SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided amethod of compacting soil. The method includes repeatedly raising a massabove the soil surface and then dropping the mass to apply impacts tothe soil surface, from the impacts on the soil surface periodicallyderiving indications of one or more instantaneous properties of thesoil, and controlling the number of subsequent impacts and/or the energyimparted to the soil at each impact and/or the frequency of the impacts,in accordance with the indicated property or properties, in order toachieve in the soil one or more predetermined properties.

The instantaneous properties for indications are periodically derivedmay include, for instance, mechanical properties such as the stiffnessor strength of the soil or the bearing capacity thereof. Alternatively,indications may periodically be derived for a property such as total orincremental soil settlement.

Preferably, a controller is used to vary one or more of the aboveparameters automatically to achieve the predetermined mechanicalproperty or properties. The controller may include a programmable logiccontroller (PLC) which is pre-programmed with one or more predeterminedmechanical properties to be attained.

In a preferred embodiment of the method, a sensor is associated with themass to provide the necessary indications. The output of the sensor isfed to the controller. This sensor may be, for instance, anaccelerometer which is arranged to monitor the deceleration of the massat each impact and which is arranged to output signals related to, forinstance, the instantaneous stiffness of the soil to the controller.

According to another aspect of the invention, there is provided a soilcompaction apparatus that includes a drop mass soil compactor. The dropmass soil compactor has a mass and a lift assembly that repeatedlyraises the mass above the soil surface and then drops the mass to applyimpacts to the soil surface. The apparatus also includes a sensorarranged to provide periodic indications of one or more instantaneousproperties of the soil, and a controller responsive to the indicationsprovided by the sensor in order to control the number of subsequentimpacts and/or the energy imparted to the soil at each impact and/or thefrequency of the impacts, thereby to achieve in the soil one or morepredetermined soil properties.

As indicated previously, the controller may include a PLC which ispre-programmed with one or more predetermined soil properties which itis desired to achieve and which is arranged to control one or more ofthe variable parameters listed above.

The apparatus of the invention may also include a position monitor,typically a global positioning system (GPS), which is interfaced withthe controller to enable the controller to exercise control over thecompaction of soil in accordance with a geographical plan.

The apparatus of the invention may be vehicle mounted and may be movablefrom a transportation orientation in which it is carried on the vehicleto an operative position in which it is located alongside the vehicle.

According to yet another aspect of the invention, there is provided amethod of measuring one or more physical soil properties on a site. Themethod includes providing on the site a drop mass soil compactor thathas a mass and a lift assembly that raises the mass above the soilsurface and then drops the mass to apply an impact to the soil surface.The method also includes measuring one or more instantaneous physicalproperties of the soil from the impact applied to the soil surface bythe mass.

Still further, the invention provides an apparatus that measures one ormore physical soil properties on a site. The apparatus includes a dropmass soil compactor that has a mass and lift assembly that raises themass above the soil surface and then drops the mass to apply an impactto the soil surface. The apparatus also includes a sensor that measuresfrom the impact applied by the mass, one or more instantaneous physicalproperties of the soil.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe invention, will be better understood when read in conjunction withthe appended drawings. For the purpose of illustrating the invention,there are shown in the drawings embodiments which are presentlypreferred. It should be understood, however, that the invention is notlimited to the precise arrangements and instrumentalities shown.

In the drawings:

FIG. 1 shows a side elevational view of a vehicle mounted drop mass soilcompaction apparatus according to this invention, the apparatus being atan operative orientation; and

FIG. 2 shows a perspective view of the apparatus of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The drawings illustrate a drop mass soil compaction apparatus 10according to this invention. In this embodiment, the apparatus 10 ismounted on the chassis 12 of a truck 14, but it will be understood thatthe apparatus could equally well be mounted on a wheeled trailer chassisdrawn by a truck or tractor, or on a track-type self-driven vehicle ortrailer.

The apparatus 10 includes a lift assembly 23 that raises and drops acompaction mass 28. The lift assembly 23 includes a frame 16 mounted forside to side traversing movement on a laterally extending traverse beam18 which is pivoted to the rear end of the truck 14 at a pivot point 20.The frame 16 includes a pair of upright support members 22 supporting arearwardly directed suspension member 26. The rearward end of the member26 is located vertically above the compaction mass 28 and a hydrauliccylinder 30 acts between the suspension member 26 and the mass asillustrated. Extending vertically from the mass 28 are guide rods 32which slide in guide cylinders 34 connected to the members 22 byinclined braces 35.

A bracket 36 connected to the support members 22 is engaged in slidablemanner with the traverse beam 18 in order to achieve the side to sidetraversing movement of the frame as mentioned above. The apparatus 10includes a drive (not shown) for driving the frame 16 from side to side.The drive could take any one of a number of conventional forms. It may,for instance, be a chain and sprocket drive, at least some components ofwhich are mounted within the bracket 36, and/or the traverse beam 18.

The drop mass soil compactor apparatus 10 is shown at an operativeorientation with the mass 28 resting on the ground. The compactorapparatus 10 will operate at this orientation during soil compactionactivities. When the compactor apparatus 10 is to be transported fromone location to another, hydraulic cylinders 38 acting between lugs 40extending from the traverse beam 18 and the chassis 12 are contracted topivot the frame 16 to a prone, generally horizontal orientation on thechassis 12.

In use, soil beneath the mass 28 is compacted by the lift assembly 23repeatedly lifting the mass 28, by contracting the cylinder 30, and thendropping the mass 28 to apply impacts to the soil surface.

Attached to the mass 28 is a sensor 42 or specifically an accelerometer42, the output of which is fed to a controller such as a programmablelogic controller (PLC) 44. The PLC 44 is shown diagrammatically in FIG.1 as a remote component, but it will be understood that in practice thePLC 44 and other ancillary equipment will form an integral part of theapparatus 10 itself. The controller or PLC 44 may include otherancillary control circuitry without departing from the invention.

As the mass 28 impacts on the soil, the deceleration which the mass 28undergoes, as measured by the accelerometer 42, provides an indicationof the instantaneous stiffness of the soil, and this in turn provides areliable, real time indication of the level of compaction of the soil.In this example, the PLC 44 is pre-programmed for the apparatus 10 toachieve in the soil a predetermined level of soil stiffness. The PLC 44,in turn, automatically controls various parameters of the compactionoperation. For instance, the PLC 44 may control the impact energyapplied to the soil at each impact. This is achieved by varying theheight to which the mass 28 is raised prior to each blow, andaccordingly, the potential energy which is stored and which is availablefor delivery to the soil, by controlling the hydraulic operation of thecylinder 30 and/or by means of appropriate mass position sensors tosense the position of the mass.

By way of example, the impact energy which is applied may be controlledby the PLC 44 to have the same value for a number of impacts, then adifferent value for a succeeding series of impacts, and so on.Alternatively, the impact energy may be varied from impact to impact orthe same energy level may be maintained throughout the compactionoperation.

The PLC 44 may also control, in accordance with its program, the numberof blows applied to the soil. As yet another possibility, the PLC 44 maycontrol the frequency of the impacts, in this case by varying theduration of each impact cycle and/or by varying the time lapse betweencycles. Although not specifically mentioned, other variable parametersmay also be controlled instantaneously by the PLC 44.

In the drawings, the numeral 50 indicates a flexible cable tray whichcarries signal transmitting wiring and/or hydraulic hoses for thecylinder 30 and its ancillary equipment such as hydraulic pumps and soon. It will also be understood that in practice a hydraulic power pack(not illustrated) will be mounted on the chassis 12.

In practice, the soil compaction apparatus 10 described above may beused to compact soil at various locations on a site, or to compact theentire site. It will be understood that the vehicle 14 can be drivenfrom one location to another on the site to enable the soil compactionapparatus to be used to compact different regions of the site. At eachstationary location of the vehicle 14, the apparatus 10 can be used tocompact a limited strip of soil, this being permitted by the ability ofthe frame 16 to traverse from side to side on the traverse beam 18 andthe maneuverability of the vehicle 14.

The soil compaction apparatus 10 described above can also be interfacedwith a positioning system, typically a global positioning system (GPS),so that indications of soil stiffness can be correlated withgeographical position. This in turn enables a site plan to be derivedwhich gives real time information related to the levels of soilcompaction at different locations on the site. It will be understoodthat integrated information regarding geographical position and level ofsoil compaction can be stored digitally and/or represented graphicallyto provide a substantially complete analysis of the state of soilcompaction across a site or selected regions thereof.

Although mention has been made of compacting soil regions over a site,the principles of the invention are equally applicable to compaction ofsingle, small areas where a specific level of compaction is required. Atypical example here would be soil compaction adjacent a fixed structuresuch as a bridge abutment or building.

Also, although specific mention has been made of monitoring soilstiffness and of varying the operating parameters to achieve a desiredlevel of soil stiffness, it is within the scope of the invention for theapparatus 10 to monitor a variety of other soil properties and tocontrol the operating parameters to achieve one or more specific,desired properties. The apparatus 10 could be arranged to monitor anyone or more of a number of other mechanical soil properties other thanstiffness, for instance soil strength and/or bearing capacity, and tocontrol the operating parameters to achieve desired properties. Stillfurther the apparatus could be arranged to monitor a soil property suchas total soil settlement at each point in time or incremental soilsettlement, i.e., the amount of soil settlement in a given period oftime or as a result of one or more impact blows.

Instead of an accelerometer 42 to monitor any particular soil property,in the above example the soil stiffness, any other suitable form ofsensor 42 could also be used. Other viable forms of sensor 42 include avelocity sensor to measure the velocity of the mass during impact, adisplacement sensor such as a displacement transducer to measure soilsettlement or a force or pressure transducer to measure the force orpressure applied to the soil surface by the mass at impact.

As mentioned previously, the principles of the invention can be used notonly to achieve and control soil compaction, but also to measureinstantaneous soil properties on a site. In this role, the apparatus 10described above may be arranged to raise and drop the mass 28 only onceat each location on the site where a measurement of instantaneous soilproperties is required. The monitoring equipment, including theaccelerometer 42 and/or additional transducers described above, are thenarranged to provide, at each such location, a measurement of a selectedsoil property, such as stiffness, settlement and so on. As in the caseof the apparatus described above, the apparatus in this role may beinterfaced with a geographical positioning system such as a GPS, therebyto provide soil property measurements for different site locations. Theinformation obtained in this way may, with appropriate signal processingequipment and associated software, be presented in the form of a map,contoured or otherwise, or in tabular form. This application may forinstance be employed by soils engineers to assist them in performingsite certification functions.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

1. A method of compacting soil comprising: repeatedly raising a massabove the soil surface and then dropping the mass to apply impacts tothe soil surface; from the impacts on the soil surface periodicallyderiving indications of one or more instantaneous properties of thesoil; and controlling at least one of the number of subsequent impacts,energy imparted to the soil at each impact and frequency of the impacts,in accordance with the indicated property or properties, a sensor beingassociated with the mass to provide the periodic indications and anoutput of the sensor is fed to a controller including a programmablelogic controller (PLC) that is pre-programmed with one or morepredetermined soil properties to be attained, the PLC operatingautomatically to vary at least one of the number of impacts, the energyimparted to the soil at each impact and the frequency of the impacts toachieve the predetermined soil property or properties.
 2. The methodaccording to claim 1, wherein indications are periodically derived ofinstantaneous mechanical or physical properties of the soil.
 3. Themethod according to claim 2, wherein the mechanical properties of thesoil include at least one of the stiffness of the soil, strength of thesoil and the bearing capacity of the soil.
 4. The method according toclaim 1, wherein indications are periodically derived from at least oneof total soil settlement and incremental soil settlement.
 5. The methodaccording to claim 1, wherein the sensor is an accelerometer associatedwith the mass and the accelerometer is configured to output signalsrelated to the deceleration of the mass at each impact to the PLC.
 6. Asoil compaction apparatus comprising: a drop mass soil compactor havinga mass and means for repeatedly raising the mass above a soil surfaceand then dropping it to apply impacts to the soil surface; and a controlmeans having a programmable logic controller (PLC) which ispre-programmed with one or more predetermined soil properties to beattained and a sensor associated with the mass to provide periodicindications of one or more instantaneous properties of the soil, the PLCbeing arranged to respond to the indications provided by the sensor andto control at least one of a number of impacts, energy imparted to thesoil at each impact and frequency of impacts of the mass, to therebyachieve in the soil the one or more predetermined soil properties. 7.The apparatus according to claim 6, further comprising: a geographicalposition monitor which is interfaced with the PLC to enable the controlmeans to exercise control over the compaction of soil in accordance witha geographical plan.
 8. The apparatus according to claim 7, wherein thegeographical position monitor is a global positioning system (GPS). 9.The apparatus according to claim 6, wherein the sensor is anaccelerometer arranged to output signals related to the deceleration ofthe mass at each impact to the PLC.
 10. The apparatus according to claim6, wherein the apparatus is configured to be vehicle mounted.
 11. Theapparatus according to claim 10, wherein the apparatus is configured tobe movable from a transportation orientation in which the apparatus iscarried on the vehicle to an operative position in which the apparatusis located alongside the vehicle.
 12. A soil compaction apparatuscomprising: a drop mass soil compactor having a compaction mass and alift assembly, the lift assembly being coupled to the compaction massand being configured to repeatedly raise the compaction mass above asoil surface and drop the compaction mass onto the soil surface; asensor having an output, the sensor detecting at least one of conditionsof the mass and conditions of the soil; and a controller that receivesthe output from the sensor and controls the lift assembly, thecontroller controlling at least one of a number of impacts, energyimparted on an impact and frequency of impacts of the compaction mass.